How to scan for a port waiting for a connection on a network

Question

I am currently working on a little chat utility in C#.
The problem is I can't figure out how to scan the network for a specific port on all machines. I am currently using this method

    IPGlobalProperties network = IPGlobalProperties.GetIPGlobalProperties();
    IEnumerable<IPEndPoint> connections = network.GetActiveTcpListeners()
                                                        .Where(x => x.Port == ConstParams.iPort);

where ConstParams.iPort is the port I want to scan (6910 here).

The problem is that the returned values are only local ports and the "0.0.0.0" ip address...

How can I scan for all open ports (6910) on the current network?

Answer 1

Rather than using port scanning, I suggest you to implement a simple discovery mechanism based on multicast/broadcast communication.

During the startup the application should broadcast/multicast its IP/Port information. All running instances should respond to this message with their IP/Port information. This kind of a discovery mechanism is easy to implement, and it is both faster in runtime and more dynamic than the port scanning approach.